When colostomy and ileostomy bags are used there is often a build up of flatus and it is desirable to include some means for releasing this. However, if a vent is provided it should also include a means for removing the unpleasant odours from the flatus. A number of ways of achieving this have been proposed in the past, including the use of a filter containing carbon particles or granules on a support. A disadvantage of this type of filter is that a long pathway is needed through the carbon for the filter to be effective.